In the field of public security such as fire control and disaster relief, a dedicated trunking communications system is used to implement communication between related staff members, so that a working progress can be reported between the staff members and the staff members can obtain a task. To ensure that staff members understand site conditions and make decisions in time, the trunking communications system is required to be capable of implementing a communications mode such as video communication that requires a high access rate, so that work such as fire control work, disaster relief work, and other work are effectively completed.
To satisfy requirements of the public security field on high-rate communication, a mobile communications network, such as a fourth-generation communications network, operated by an operator is enhanced in the prior art, so that the mobile communications network supports trunking communications. Therefore, high-rate access provided by the mobile communications network can be used in trunking communications to satisfy public security requirements. Specifically, a terminal used for trunking communications accesses a mobility management entity and a gateway device by using a radio access network, and further accesses a trunking communications server by using a gateway. The trunking communications server that is responsible for call management of trunking communications, management of trunking group members, and the like sends trunking communications information (including a voice, a video, and the like) to the terminal in a multimedia broadcast multicast service (Multimedia Broadcast Multicast Service, MBMS) manner or in a unicast manner.
In the foregoing technical solution, the terminal used for trunking communications is required to be located in network coverage and access the mobile communications network. However, in a practical trunking communications application, for example, in a fire rescue scenario or another scenario, it is impossible that all terminals are located in the network coverage. Consequently, a terminal outside the network coverage is incapable of using a trunking communications function by means of the mobile communications network; in this case, staff members cannot report situations of a working site in time, obtain a task, or the like, and communications reliability is low.